Even before the widespread demand for pollution abatement in industry, much activity was devoted to the removal of sulfur dioxide from waste gases because of its destructive tendencies. Many different approaches have been tried both before and since the increased interest in pollution abatement. However, sulfur dioxide is one of the most pervasive pollutants in industry, and its removal is accomplished only at significant economic penalty.
As examples of patents disclosing various approaches to the removal of sulfur dioxide from stack gases, the reader may be interested in reviewing Eustis, U.S. Pat. No. 1,589,133, Johnstone et al, U.S. Pat. No. 2,161,056, Suriani et al, U.S. Pat. No. 3,574,530, Potts U.S. Pat. NO. 3,630,672, Villers-Fisher et al, U.S. Pat. No. 3,632,306, and Urban, U.S. Pat. No. 3,644,087. Of interest also in the context of the following disclosure will be U.S. Pat. Nos. 3,401,014, 3,421,848 and 3,632,307 to Saeman, Popovici et al and Cornelis van Es et al, respectively. The patent to Potts may be of particular interest because of its use of potassium polyphosphate to absorb sulfur dioxide. The reader may also be interested in the following literature articles:
Volume 6, Environmental Science and Technology, "SO.sub.2 Removal Technology Enters Growth Phase," pages 688-691; Slack and Falkenberry, "Sulfur Oxide Removal From Waste Gases: Lime-Limestone Scrubbing Technology," Volume 22, APCA Journal No. 3, March, 1972, pages 159-166; Horlacher et al, "Four SO.sub.2 Removal Systems," Volume 68, Chemical Engineering Progress, pages 43-50; Bonnifay et al, "Partial and Total Sulfur Recovery," Volume 68, Chemical Engineering Progress, August, 1972, pages 51-52; Potter and Craig "Commercial Experience with an SO.sub.2 Recovery Process," Volume 68, Chemical Engineering Progress, pages 53-54; and Brown et al, "SO.sub.2 Recovery with Activated Carbon," Chemical Engineering Progress, Volume 68, pages 55-56. Also of interest may be U.S. Pat. No. 3,671,189 to Betts.